tech(opentsdb): add init ref for opentsdb

pkg/cmd/grafana-server/main.go

@@ -20,6 +20,7 @@ import (
 	_ "github.com/grafana/grafana/pkg/services/alerting/conditions"
 	_ "github.com/grafana/grafana/pkg/services/alerting/notifiers"
 	_ "github.com/grafana/grafana/pkg/tsdb/graphite"
+	_ "github.com/grafana/grafana/pkg/tsdb/opentsdb"
 	_ "github.com/grafana/grafana/pkg/tsdb/prometheus"
 	_ "github.com/grafana/grafana/pkg/tsdb/testdata"
 )